The invention relates to improvements in windshield wiper mechanisms for operation in cold weather. The problem of the formation of ice leading to the stoppage of either the pressure mechanism or the effective squegee action of the wiper blade is a serious one for the average family car but especially so for trucks and other vehicles which must continue to operate during snowstorms. Heated air supplied to the windshield from the interior of the car is generally inadequate in severe wintry conditions.
Many solutions have been attempted by supplying heat directly to the wiper system. These include embedding electric resistance elements in the wiper blade as in U.S. Pat. Nos. 3,718,940 and 3,936,901. Another approach is to supply heat to the backing member which grips the wiper blade. U.S. Pat. No. 3,408,678 does it by making the backing member itself a nichrome resistance element while U.S. Pat. No. 3,530,525 provides a heating wire in contact with the metal backing element.
A further solution has been attempted by forming envelopes about the wiper parts as in U.S. Pat. No. 3,523,626 where both the supporting pressure applying mechanism and a major portion of the wiper blade are enclosed in an envelope containing a liquid which is electrically heated. In U.S. Pat. No. 3,619,556, a heating element embedded in the wiper blade is in contact with a portion of an envelope which encloses the backing element and an upper portion of the wiper-blade.
The foregoing attempted solutions are inadequate for various reasons. In modifications involving embedded resistance elements in the wiper blade, the latter is stiffened and does not flex properly when in operation. The heat produced tends to be excessive and quickly deteriorates the rubber of the blade. When the wiper blade needs replacement, it is expensive to replace the unit with the resistance element being discarded too. Where heat is applied to the backing element, it is not sufficiently close to the squegee portion of the wiper blade. In other modifications, the envelopes are bulky, presenting flexing problems and are expensive.
Accordingly it is the primary object of this invention to provide an improved heating unit which may be adapted to existing windshield wiper mechanisms and wiper blades and provide heat to both, sufficient to prevent ice formation causing malfunction of the wiper assembly.
Another object of this invention is to provide an improved hearting unit which is flexible and allows full normal flexure of the wiper blade.
A further object of this invention is to provide an improved heating unit having a heat sensitivity control unit to prevent the overheating of the wiper blade.
A still further object of this invention is to provide an improved heating unit for a windshield wiper which is relatively inexpensive and allows normal wiper blade replacements to be made without discarding the electric resistance element.